In the ensuing description, familiarity with ESR spectrographic microanalysis and the availability and utilization of spin labels in such analysis will be assumed. Further background is provided in Spin Labeling, Theory and Applications Vols. I and II, 1976, 1979, edited by Lawrence J. Berliner, published by Academic Press, New York. This invention makes use of spin labeling techniques to prepare target entity specific sample means, which upon contact with the target entity will characteristically generate free radicals of the spin resonating type, e.g. by displacement, as a function of the target entity presence. These specific sample means are packaged in a particular novel manner according to the invention enabling controlled exposure to the ambient fluid of interest while minimizing spurious spin resonant response, by the selective exclusion of nontarget ambient medium constituents, for example; and thereafter the invention effects measurement of the exposed sample target entity presence by subjecting the sample in its original exposed state to appropriate milliwatt levels of microwave energy at an appropriate frequency, e.g. 9.20 GHz. and sensing and recording the tumbling of the spin resonating free radicals.
There has been much written on the microanalytic uses of spin resonance phenomena, by the selective spin labeling of one or another reagent, for selective, detectable reaction, and such knowledge is a prerequisite to the invention disclosed here, wherein such knowledge is made immensely more useful than mere laboratory usage, by disclosure of the means to take the accumulated information out of the laboratory and into the field where needed measurements can be made and acted upon immediately to protect workers and the environment, and to assist industry in finding new sources of scarce materials at minimum cost and effort.
Integral to the present invention is the use of a microwave generator. Various of these have been proposed and built. Presently preferred for use in carrying out the present invention is a modification of the so-called IMPATT diode device, the basic form of which is described in articles by Hogg, Applications of IMPATT Diodes as rf Sources for Microwave EPR Spectroscopy Rev. Sci. Vol. 44, No. 5, pp. 582-587, May 1973; and A Low Cost X-Band IMPATT Diode Marginal Oscillator for EPR Amer. J. Phys. Vol. 41, pp. 224-229, February, 1973. An important feature of the invention is the modification of the Hogg type device to enable field use and the provision of the sample means adapted to perform with the thus modified device, to realize the objects of the invention.